This invention relates to thin film magnetic heads, and more particularly relates to such heads having a magnetoresistive sensing element (MRE) located inwardly from the head face, referred to herein generally as magnetoresistive heads; and also relates to a method of producing such heads, and to integrated structures incorporating them.
Magnetoresistive heads typically include a strip-shaped element of a ferromagnetic, metallic, magnetically anisotropic material, for example NiFe, commercially known as Permalloy, which is deposited as a thin film on a substrate and positioned either with one of its edges in the immediate proximity of a magnetic recording medium such as a tape, or alternatively, remotely from the medium with a flux guide arranged to bring the magnetic fields of the medium to the element. The fields of the recording medium produce variations in the magnetization of this magnetoresistive element (MRE) and thereby modulate the resistance of the element via the magnetoresistive effect. In order to measure the changing resistance of the MRE, the element is electrically biased. This is typically done by directing an electric current through the element. Detection circuitry is then connected to the element so that the changing resistance of the element can be monitored to produce an output which is representative of the information stored on the medium.
Thin film magnetoresistive heads are being developed which offer the advantages of miniaturization and integration on a single substrate. In the case of magnetic audio tape, information is written onto, and read from, spaced, parallel tracks on the tape. To increase information density, the width of the tracks, as well as the spacing between the tracks, can be reduced. For example, in the newly proposed audio format for digital compact cassettes (dcc), there are a total of 18 separate, parallel tracks on a tape having the same width as the conventional compact cassette tape.
In order to achieve magnetic heads having correspondingly small dimensions, such heads are now being developed using thin film processing techniques of the type used to manufacture integrated circuits in silicon substrates.
Not surprisingly, problems arise in the manufacture of such heads which are similar to problems encountered in the fabrication of some multilayer integrated circuits. For example, as the size of the heads is reduced, the thicknesses of the various layers become more significant. Particularly at the edges of layers, problems known as "step coverage" can occur. For example, inadequate coverage of a step of a conductive layer by an insulating layer can lead to damaging shorts between the conductive layer and an overlying conductive layer. Conversely, inadequate coverage of an insulating step by a conductive layer can lead to discontinuities in the conductive layer.
In the case of thin film heads having broken flux guides, the edges of the flux guide sections can give rise to such step coverage problems. For example, a thin test/bias conductor is typically formed on the insulating layer which covers the flux guide sections. Inadequate step coverage at the edges of the flux guide sections can lead to shorts between one or both of these sections and the test/bias conductor. Furthermore, the insulating layer itself will have steps, caused by following the contours of the underlying structure. Inadequate coverage of these steps by the test/bias conductor layer can cause discontinuities in this layer.
A problem associated with prior art magnetoresistive heads has been the presence of Barkhausen noise in the output of the heads caused by the erratic movement of magnetic domain walls in the MRE and their associated flux guides in response to the changing magnetic fields of the tape. Such Barkhausen noise in the MRE can be substantially eliminated by maintaining single domain magnetization in the read portion, or active region, of the MRE. However, stability of this single domain structure can be jeopardized by mechanical stresses in the MRE, caused for example, by stresses in adjacent layers created during manufacture.
The stability of the flux guides can be increased by increasing their thickness, thereby making it more difficult to move the domain walls. However, such a measure aggravates the step problem described above.